This has got to be one of the most fun things I’ve done on the internet: answering anonymous search queries with actual posts. I have no idea why I find this so satisfying, but it’s a blast.
This question is a relatively complicated one. I’ll try to break it down. It’s worth noting that a lot of this advice is style-dependent. I’ll try to note major divergences from these guidelines that I’m aware of, but you should always consult the guidelines for your style when determining when a beer is ready.
There are two stages at which this question might be asked:
- At the end of fermentation, when the beer is ready to be conditioned. For a homebrewer, this is typically the end of the secondary fermentation.
- At the end of conditioning, which is the process of carbonating the beer and preparing it for storage. Homebrewers typically bottle-condition their beers or force-carbonate using CO2 systems and kegs.
So first: How do you know when your beer is done fermenting and ready for the conditioning phase?
Following the classic “1-2-3″ rule will get you good results for most styles of beer as a home brewer. This means your beer should spend 1 week in primary fermentation (usually a plastic bucket), 2 weeks in secondary fermentation (usually a glass carboy), and 3 weeks in bottles.
Primary fermentation is primarily for alcohol production, while secondary fermentation is mostly useful for allowing particulate matter to flocculate or come out of solution and float to the bottom (or top) of the fermentation vessel. The time in bottles allows hops to mellow and carbonation to build.
How to know when each stage is finished:
- Primary fermentation: Primary fermentation is done when the beer has reached about 90% of its maximum attenuation. Most yeasts have attenuation levels of around 75%. So if after your boil, you measured your gravity at 1.048, and after primary fermentation your beer is at 1.012, you’ve hit 75% attenuation and are probably done. If you’re sitting around 1.014, you’re probably also ready to rack to secondary. If the liquid is around 1.020, you might give it another day in the primary. Note that “attenuation” is just a more exact way of describing alcohol content, so what you’re really determining here is the alcohol content of your beer. More alcohol means less sugar (desirable for most styles).
- Secondary fermentation: Secondary fermentation is really finished whenever you want it to be. You should be mostly looking for clarity of the liquid. Secondary fermentation will allow residual protein, dead yeast, and floating hops to sink to the bottom of the vessel, easily allowing you to filter these things out when you bottle. You can also taste the beer to determine if the hop character should mellow a bit more before bottling.
- A quick note: I usually siphon my beer from the secondary into a third vessel at bottling time, just to make sure I don’t accidentally put a bunch of the muck from the bottom of the secondary vessel into my bottles.
- Bottling: The only way to really know if your bottles are ready is to chill one and try it. Most styles will carbonate in 2-3 weeks given adequate addition of bottling sugar. You can speed this up significantly by pitching additional yeast at the same time that you pitch the bottling sugar. If you do this, your beer should carbonate in approximately a week.
Notable exceptions that I can think of:
- American Hefeweizen, and most hefs in general, don’t need secondary fermentation. The style guidelines call for suspended yeast content, and hef yeasts from Wyeast and White Labs will usually remain suspended in liquid for a good long time, making secondary fermentation unnecessary at best.
- Some styles, notably lagers, and particularly high-protein lagers like Octoberfest and wheat lagers, require additional phases during secondary fermentation. A “diacetyl rest” is a common step along this vein, and is described nicely by John Palmer.
- Some styles, notably Hefeweizen because of the suspended yeast contents, will carbonate extremely quickly in bottles even without additional yeast additions, usually in less than a week.
- Alcohol is lighter than water, so attenuation readings might be wrong for high-gravity beers. There are lots of suggestions about how to combat this as a home brewer, but leaving your high-gravity worts in primary fermentation, pitching extra yeast, or re-pitching extra yeast into primary after a few days never hurt anyone.
- If you’re kegging, you can “force carbonate” your beer using a CO2 system. This can result in a carbonated beer after just a couple days, but should not be confused with faster-than-normal conditioning.
- High-hop styles like IPAs will still benefit from a period of hop mellowing. Hop mellowing is useful for subduing the sharp, fresh hop flavor that most people find undesirable. If you’re worried about losing hop aroma, you can pitch hops directly into the secondary fermentation vessel (called “dry hopping”).
I’m sure I missed a lot — there’s a lot about this that is style-specific, and a lot about it that touches on subjects that are way out of scope for this brief post (and that are better covered in better literature!).
Hope it helps at least one person figure out when they can drink their beer!